1. Technical Field
The invention relates generally to a metal pouring apparatus and more particularly to such apparatus equipped with an induction heater.
2. Prior Art
Automated pouring devices have been used for many years to produce metal castings. Such devices typically include a pouring vessel having an inlet for admitting molten metal into a main holding chamber within the vessel and a bottom nozzle outlet for discharging the metal into underlying casting molds. Such vessels are commonly equipped with an automated stopper rod mechanism for regulating the discharge of metal from the nozzle.
The earliest of these pouring vessels was unheated. Consequently, when the metal temperature fell below a minimum pouring temperature, the metal in the ladle had to be pigged or else scrap castings would be produced.
Subsequent pouring vessels were equipped with a cored channel induction heater. The metal in this vessel is heated by withdrawing it from the vessel's main chamber, passing the metal through the induction heated channel for heating and then back into the main chamber for mixture with the remaining metal in the vessel. While this type of heated pouring vessel performs well when pouring most types of ferrous metals, including gray and malleable iron, it is not well suited for pouring magnesium-treated ductile iron, since MgO deposits quickly plug the channel inductor and render it useless. There have been recent efforts by those skilled in the metal pouring industry to overcome the plugging problem, however, most producers of cast ductile iron products have reverted to using unheated pouring vessels.
Various other induction heating arrangements have been proposed as alternatives to channel inductors. One such alternative utilizes a coreless induction coil extending vertically about a bottom poured holding vessel having a vertical holding chamber. This vessel, however, is open at the top to the atmosphere and is unsuitable for pouring treated ductile iron since atmospheric exposure depletes the magnesium content of the iron. A similar known pouring system uses the same type of vertical pouring vessel but is fitted with a horizontal coreless inductor extending from a side of vessel and forming an auxiliary horizontal heating chamber into which metal is withdrawn from the main chamber of the vessel for heating before being returned to the main chamber. This vessel is also open to the atmosphere at the top and as such is not suitable for pouring treated ductile iron. Furthermore, this system is not known to be successful in pouring treated ductile iron since the inductor tends to plug with deposits, like the cored induction heater. Its known usage has been limited to nonferrous applications.
The U.S. Pat. No. 5,056,692 to Wilford et al., granted Oct. 15, 1991, discloses still another alternative whereby a horizontal flow-through bottom poured vessel is equipped with a vertical tower coupled to a vacuum for withdrawing molten metal from the vessel upwardly into the tower to establish a metal pressure head. Vertically extending coreless induction coils surround the tower for heating the metal during downtimes or pour stoppages. This type of induction heater, however, detracts from the inherent flow-through pouring capability of the vessel by requiring metal to be withdrawn from the vessel for heating prior to pouring. Metal thus can not be heated simultaneously with the pouring of the metal.
Coreless induction heaters have found many applications in various industries, including incorporation in an induction melting furnace developed previously by William J. Duca, one of the inventors herein, forming the subject matter of U.S. Pat. No. 3,602,625, granted Aug. 31, 1971. This furnace includes a U-shaped chamber and a surrounding coreless induction heating coil for melting and heating the metal as it flows through the chamber. Such a furnace, however, is limited to melting and heating metal and is not suited for dispensing metal into molds.
In the metal casting industry, melting and pouring are considered and treated as separate, nonanalogous arts. This is evidenced by the fact that for over 20 years nobody in either industry, including Duca himself, thought to use an induction heater like that disclosed in the Duca '625 patent in combination with a pouring vessel as a means of possibly overcoming the plugging problems associated with pouring treated ductile iron through an induction heated vessel. In fact, during this 20 year time period, much of Duca's efforts involved redesigning existing channel-type inductors to accommodate treated ductile iron.
It was not until the joint inventors herein collaborated that they discovered using an induction heater of the type previously developed by Duca for melting furnace applications in combination with a modified existing flow-through pouring vessel as a means of solving the plugging problems associated with pouring treated ductile iron without interfering with the continuous pouring cycle of the vessel.